1. Field of the Invention
The present invention relates to surgery. More particularly, the invention relates to surgical instruments used in performing surgery in the middle ear, and specifically for handling ossicular prostheses implantable in the middle ear.
2. State of the Art
Hearing is facilitated by the tympanic membrane transforming sound in the form of acoustic sound waves within the outer ear into mechanical vibrations through the chain of ossicles (malleus, incus, stapes) in the middle ear. These vibrations are transmitted through the ossicles to the lower footplate of the stapes where micro or macro motion of the footplate results in compression waves within the fluid of the inner ear. These compression waves lead to vibrations of the cilia (hair cells) located within the cochlea where they are translated into nerve impulses. The nerve impulses are sent to the brain via the cochlear nerve and are interpreted by the brain as sound.
Hearing efficiency can be lost to erosion of the ossicular bones. Various combinations or portions of the bones can be replaced. For example, all of the ossicles between the tympanic membrane and the stapes footplates can be replaced using a total ossicular replacement prosthesis, or TORP. A TORP includes a proximal disc-like head in contact with the tympanic membrane, a longitudinal shaft, and a shoe at a distal end for contacting the footplate of the stapes, and distributing the force from the head end at the tympanic membrane to the shoe at the distal end positioned on the footplate. Alternatively, the malleus and incus can be replaced leaving all or a portion of the stapes intact. The prosthesis for such a procedure is a partial ossicular replacement prosthesis, or PORP. A PORP also includes a head for placement at the tympanic membrane and includes bell or cup that seats over the capitulum and/or junction of the crura of the stapes. As yet another alternative, the stapes can be replaced, leaving the malleus and incus substantially intact. The determination of which one or more ossicles is to be replaced with a prosthesis is determined based on the cause of the hearing loss, the quality of the ossicles, and the judgment of the surgeon.
Regardless of which prosthesis is determined to be appropriate and selected for implantation, the prosthesis is extremely small. Typically, dimensions for the prosthesis range from 3 to 7 mm in length and a shaft diameter of less than 1 mm. The surgeon uses a tool to engage and manipulate the prosthesis into position within the middle ear structure. Known tools include a mechanical grasper and a suction tip to place and position ossicular prostheses. These tools are elongate, with a distal implant manipulating end of the instrument significantly displaced from the proximal hand-holdable portion. This amplifies motion from the surgeon's handle to the distal end, where steadiness is desirable.
When using a mechanical grasper, in order to release the prosthesis, a force is applied at the proximal handle end to move parts of the grasper relative to each other, which is then amplified as movement at the distal end. This amplified and often uncontrolled movement, can result in displacement of the prosthesis. Also, if a prosthesis held by a mechanical device is inadvertently contacted during insertion, it can be damaged if held too tightly by the device, or can be dropped or displaced out of intended orientation; it is very difficult to reengage or reorient the prosthesis once displaced from its position in the grasper once the distal end of the grasper is located within the middle ear.
Instruments that use suction to hold a prosthesis have the advantage in that mechanical forces are not required at the proximal end of the device to release the implant; thus, such forces cannot be amplified to displace the prosthesis from the intended target and release of the prosthesis should be more precise. However, current suction instruments do not have the ability to maintain implant position and/or re-orient a prosthesis in the event the prosthesis is inadvertently displaced from its initial position. If the prosthesis is off-position, approaching the anatomy for implantation may be difficult or impossible.